1. Field of the Invention
The present invention relates to an optical disk producing sheet, and more particularly to an optical disks producing sheet on which concavoconvex pattern of the stamper is transferred and pits or grooves are formed.
2. Description of the Related Art
The following method has been disclosed as a method for producing optical disks (Japanese Patent No. 2956989).                (a) A dry photohardenable film is laminated to an optically transparent substrate having stable dimensions.        (b) A reflective layer is optionally formed on the exposure surface of the dry photohardenable film.        (c) The exposed surface of the photohardenable film is embossed with relief information tracks by the application under pressure of a stamper containing a relief image of an information track.        (d) Actinic rays are passed through the transparent substrate and the photohardenable film while these are kept in contact with the stamper, and the photohardenable film is cured.        (e) The stamper is detached from the embossed and hardend film.        (f) A light reflecting layer is formed on the embossed surface of the hardened film.        
The following compounds may be used for the composition constituting the dry photohardenable film: diacrylate ester of a bisphenol A epoxy resin derived from bisphenol A and epichlorohydrin, trimethylol propane trimethacrylate, optical brightening agents, 2-mercaptobenzoxazole, 2,2′-bis-(o-chlorophenyl)-4,4′5,5′-tetraphenyl biimidazole, trimethylol propane, glycerol triacetate, methoxy hydroquinone, thermal inhibitors, diethylhydroxylamine, ethyl acrylate (57%)/methyl methacrylate (39%)/acrylic acid (4%) copolymer, ethyl acrylate, ethyl acrylate (17%)/methyl methacrylate (71%)/acrylic acid (12%) copolymer, polycaprolactone, and zinc acetyl acetonate (Japanese Patent No. 2956989, Example 1).
The dry photohardenable film is a mixture of a polymer component for shape preservation, a photopolymerizable component for curing, a low-molecular-weight component for improving the pressure deformation in the embossing process, and other additives. In a mixing example such as that described above, the low-molecular-weight component does not contribute at all to the curing reaction, and remains in the hardened film in a low-molecular-weight form even after the photocuring. In addition, since the photopolymerizable component has a comparatively low molecular weight, the unreacted photopolymerizable component remains in the dry photohardenable film in a low-molecular-weight form.
If a large amount of the low-molecular-weight component remains in the cured dry photohardenable film, the internal strength of the film is lowered and microscopic ruptures are produced in the boundary area with the stamper when the film and the stamper are detached from each other. The ruptured dry photohardenable film deposits on the stamper, and the stamper becomes contaminated.
When the dry photohardenable film component deposits on the stamper in this manner, not only does the number of times that the stamper has to be cleaned in order to transfer an accurate concavoconvex pattern increase, but the stamper life decreases and the producing cost of the optical disks increases.